Carbon fiber formed from chlorinated polyvinyl chloride, and method for preparing same

ABSTRACT

Provided is a carbon fiber that has an average fiber diameter of 1-100 μm and is a product obtained by spinning a solution of chlorinated polyvinyl chloride to obtain a chlorinated polyvinyl fiber, elongating the chlorinated polyvinyl fiber without an oxidative stabilization process, and then preheating and carbonizing the elongated polyvinyl chloride fiber. Also, provided is a method for preparing a carbon fiber which has excellent mechanical properties and a high degree of orientation without oxidative stabilization.

TECHNICAL FIELD

The present invention relates to a carbon fiber formed from chlorinated polyvinyl chloride and a method for preparing the same, and more particularly to a carbon fiber obtained by carbonizing chlorinated polyvinyl chloride as a starting material, and a method for preparing the same.

BACKGROUND ART

Carbon fiber is very valuably used as a reinforcing fiber for composite materials in general industrial applications such as automobiles, civil engineering, construction, pressure vessels, windmill blades, etc., as well as high-tech industry fields such as sports, aviation, aerospace. etc. Out of commercialized carbon fibers, a carbon fiber using polyacrylonitrile (PAN), pitch and cellulose as a precursor is prepared by spinning the precursor to obtain a fiber for a carbon fiber precursor, heating the resultant fiber under an oxidative atmosphere, carrying out an oxidative stabilization process to convert the fiber into an anti-flammable fiber so as to prevent a fiber shape from being deformed and destroyed in a further process of carbonization and graphitization, and heating the anti-flammable fiber under an inert atmosphere to carry out a carbonization and graphitization process.

However, the oxidative stabilization process described for the preparation of a carbon fiber carries out oxidation over a long period of time in order to express the strength of the prepared carbon fiber. In case of a PAN-based carbon fiber, oxidation is performed for a long time in a relatively high elongation state, which is known a main reason for longer preparation and costs. Also, an oxygen functional group and crosslink applied to this oxidation process can cause defects on the surface and inside of the carbon fiber generated during a carbonization and graphitization process, thus inhibiting the final crystallinity and physical properties of the carbon fiber.

DISCLOSURE Technical Problem

Accordingly, a technical object of the present invention is to provide a carbon fiber with excellent mechanical properties and a method for preparing the carbon fiber by using chlorinated polyvinyl chloride without a stabilization process by oxidation.

Technical Solution

To achieve the above technical object, the present invention provides,

a carbon fiber that has an average fiber diameter of 1 to 100 μm and is obtained by spinning a solution of chlorinated polyvinyl chloride to obtain a chlorinated polyvinyl chloride fiber, elongating the chlorinated polyvinyl chloride fiber without an oxidative stabilization process, and preheating and carbonizing the elongated polyvinyl chloride fiber.

The average fiber diameter may be 10 to 20 μm, tensile strength may be 1000 to 2500 MPa, and tensile modulus may be 70 to 140 GPa.

To achieve another technical object of the present invention, there is provided a method for preparing a carbon fiber that has an average fiber diameter of 1 to 100 μm, the method including: spinning a solution of chlorinated polyvinyl chloride (CPVC) to obtain a chlorinated polyvinyl chloride fiber;

elongating the chlorinated polyvinyl chloride fiber without an oxidative stabilization process to prepare an elongated chlorinated polyvinyl chloride fiber;

preheating the elongated chlorinated polyvinyl chloride fiber at 150 to 450° C. under an inert gas atmosphere; and

carbonizing the preheated product at 950 to 2000° C.

Advantageous Effects

According to the present invention, it is possible to obtain a carbon fiber that has excellent mechanical properties and elongation rate without a stabilization process by oxidation.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing the results of thermogravimetric analysis on polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC).

FIG. 2 is a view showing the results of thermogravimetric analysis on a CPVC fiber obtained by spinning a solution according to Example 1.

FIG. 3 is a view showing a ¹³C-NMR spectrum of intermediate products, in which polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC) and CPVC fiber are carbonized at 200° C., 400° C. and 1000° C.

FIGS. 4 and 5 are views showing the results of scanning electron microscopic analysis on a carbon fiber obtained according to Example 1 and a carbon fiber obtained according to Comparative Example 1, respectively.

MODE FOR INVENTION

Hereinafter, a carbon fiber obtained by using polyvinyl chloride of the present invention and a method for preparing the same will be described in more detail.

There is provided a method for preparing a carbon fiber having an average fiber diameter of 1 to 100 μm, the method including: spinning a solution of chlorinated polyvinyl chloride (CPVC) to obtain a chlorinated polyvinyl chloride fiber; elongating the chlorinated polyvinyl chloride fiber without an oxidative stabilization process to prepare an elongated chlorinated polyvinyl chloride fiber; preheating the elongated chlorinated polyvinyl chloride fiber at 150 to 450° C. under an inert gas atmosphere; and carbonizing the preheated product at 950 to 2000° C.

To carry out spinning the solution of CPVC, a composition for solution spinning may be prepared first by adding and mixing chlorinated polyvinyl chloride in at least one solvent selected from N,N-dimethylformamide (DMF), dimethylacetamide (DMAc), tetrahydrofuran (THF), nitric acid, sulfuric acid, dimethyl sulfoxide and dioxane. Solution spinning may be performed by using the composition for solution spinning obtained as above.

Out of the composition for solution spinning, a content of chlorinated polyvinyl chloride may be 1 to 90 wt %, preferably 10 to 50 wt %, and more preferably 20 to 35 wt %. And, a viscosity of the composition for solution spinning may be about 10 cP to about 100,000 cP. In this case, a conventional device used for solution spinning may be used.

In the present invention, chlorinated polyvinyl chloride, which is known as a flame retardant, may be used as a carbon fiber precursor and may go through sequential processes of elongating the CPVC fiber obtained by spinning a solution of CPVC without an oxidative stabilization process, and preheating and carbonizing the elongated polyvinyl chloride fiber. In the preparation method of the present invention, a fibrous form may be maintained during heat treatment at a high temperature for carbonization just by preheating the CPVC fiber without an oxidative stabilization process as described above. Thus, the carbon fiber obtained according to the preparation method of the present invention may have a clean surface without any defects on the surface and inside thereof by oxidation and may be an isotropic carbon fiber, but having a high degree of fiber axis orientation of graphite crystallites similar to that of a PAN-based carbon fiber. Thus, the carbon fiber may show not only mechanical properties such as relatively high strength, elastic modulus and the like, but also less preparation costs and preparation time compared to a conventional carbon fiber.

As described above, in order to maintain the fibrous form during heat treatment at a high temperature for carbonization just by preheating the CPVC fiber without the oxidative stabilization process, the properties and the like of the CPVC, which is a starting material, need to be controlled and a process of elongating the CPVC fiber needs to be adjusted before the preheating.

In the chlorinated polyvinyl chloride, a content of chlorine may be 57.7 to 84.5 wt %, for example, 63 to 68 wt % and an average degree of polymerization may be 400 to 800, for example, 600 to 700. And, the fluidity of chlorinated polyvinyl chloride may be 0.005 cc/sec or more, for example, 0.007 to 0.05 cc/sec. In case of using the chlorinated polyvinyl chloride having the properties as above, it is possible to prepare a carbon fiber that has excellent spinnability and thermal contraction properties and excellent mechanical properties and elongation rate with the oxidative stabilization process. The average degree of polymerization of CPVC was obtained by dissolving 200 g of resin in 50 ml of nitrobenzene, measuring a specific viscosity of the resultant polymer solution in a 30° C. constant-temperature bath by using an Ubbelohde viscometer, and calculating the resultant specific viscosity according to JIS-K6720-2.

An average fiber diameter of the solution-spun chlorinated polyvinyl chloride fiber may be in a range of 30 to 100 μm, for example, 35 to 55 μm. When the average fiber diameter of the solution-spun chlorinated polyvinyl chloride fiber is in the range described above, it is possible to obtain a carbon fiber having a desired elongation rate and excellent mechanical properties without a partial destruction of a fibrous form in subsequent processes.

When preparing a chlorinated polyvinyl chloride fiber as described in the present invention, it is possible to prepare a continuous long fiber having an average fiber diameter of 1 to 100 μm, which is not a short fiber having a length of dozens cm, by using solution spinning. As such, in case of preparing a composite material along with a polymer resin, very excellent tensile strength may be secured due to continuity of the chlorinated polyvinyl chloride fiber. In case of applying other spinning methods to CPVC than solution spinning, it is difficult to prepare a continuous long fiber while satisfying the average fiber diameter described above.

In the elongating of the chlorinated polyvinyl chloride fiber, the solution-spun chlorinated polyvinyl chloride fiber may be elongated in air at a temperature of 120 to 150° C., for example, 130 to 140° C. When carrying out elongation, an elongation rate is not particularly limited, but the elongation may be performed within a range in which the solution-spun chlorinated polyvinyl chloride fiber is not cut. The elongation may be performed in such a way that the elongation rate of the solution-spun chlorinated polyvinyl chloride fiber may be 0.01 to 200%, for example, 100 to 200%, for example, 150 to 200% at a temperature of 120 to 150° C., for example, 130 to 140° C. in air. As such, in case of carrying out elongation before preheating, it is possible to obtain a chlorinated polyvinyl chloride fiber with an improved tensile strength by controlling an average fiber diameter to be within a desired range, and it is also possible to prepare a carbon fiber that has a smooth surface without defects, etc. in a finally obtained carbon fiber or without a partial destruction of a fibrous form during a carbonization process and has excellent mechanical properties such as tensile strength and elastic modulus.

The preheating of the elongated chlorinated polyvinyl chloride fiber may be performed at 150 to 450° C., for example, 300 to 450° C. under an inert gas atmosphere. Then, the preheated product may be carbonized.

The carbonizing refers to a process of heat-treating the preheated carbon fiber at a high temperature of 950 to 2000° C., for example, 950 to 1100° C. This carbonization process may be performed under an inert gas atmosphere such as nitrogen, argon, etc.

During the preheating, a heating rate may be 1 to 5° C./min and a preheating time may be variable depending on a preheating temperature, which may be, for example, 0.1 to 3 hours. And during heat treatment at a high temperature, a heating rate may be 1 to 50° C./min and a time for heat treatment at a high temperature may vary depending a temperature for the heat treatment, but may be, for example, in a range of 0.1 to 3 hours.

According to one embodiment, an elongation process may be performed in such a way that an elongation rate may be 0.1 to 5.0% in a carbonization process.

According to the method for preparing a carbon fiber of the present invention, it may be fine to omit an oxidative stabilization process compared to the case of using other carbon fiber precursors. Thus, a preparation process may become simple and preparation costs and time may be reduced with a high yield.

Further, there may be provided a carbon fiber that has an average fiber diameter of 1 to 100 μm and is obtained by spinning a solution of chlorinated polyvinyl chloride to obtain a chlorinated polyvinyl chloride fiber, elongating the chlorinated polyvinyl chloride fiber without an oxidative stabilization process, and preheating and carbonizing the elongated polyvinyl chloride fiber.

The carbon fiber may be obtained according to the method for preparing a carbon fiber as described above. An average fiber diameter of the carbon fiber may be 1 to 100 μm, for example, 10 to 20 μm. And, the carbon fiber may not only have very excellent mechanical properties with a tensile strength of 1000 to 2500 MPa and a tensile modulus of 70 to 140 GPa, but also have a high degree of crystallinity and a high degree of fiber axis orientation of carbon or graphite crystallites in the range of 60 to 80% with regard to the fiber axis.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1

CPVC (H-17 grade, degree of polymerization (DP, JIS K 6720-2): 750±50 and content of chlorine: 63 wt %, Hanhwa Chemical Co. Ltd.) was dissolved in a mixed solvent of tetrahydrofuran and N,N-dimethylformamide at a volume ratio of 1:1 so as to prepare 30 wt % of a carbon fiber precursor solution.

The carbon fiber precursor solution was subjected to wet solution spinning in acetone and vacuum-dried at 120° C. so as to obtain a CPVC fiber having an average fiber diameter of about 51 μm. The CPVC fiber having an average fiber diameter of about 51 μm was elongated 150% at 140° C. to obtain the CPVC fiber having an average fiber diameter of 42 μm, after which a preheating process was performed under a nitrogen atmosphere by raising a temperature up to 450° C. at a heating rate of 3° C./min and heat-treating the elongated CPVC fiber for 30 minutes. Then, the resultant product, which underwent the preheating process, was subjected to carbonization by raising a temperature up to 1000° C. at a heating rate of 5° C./min and heat-treating the product at that temperature for 10 minutes so as to prepare a CPVC carbon fiber. The carbon fiber prepared as above had an average fiber diameter of 16.2 μm. The average fiber diameter of the carbon fiber was measured by using a laser measuring instrument (M550A; Anritsu Devices Co. Ltd.).

Example 2

A carbon fiber was prepared according to the same method as shown in Example 1 with an exception of changing an elongation rate of the CPVC fiber into 200% in the process of elongating the CPVC fiber having an average fiber diameter of about 51 μm. An average fiber diameter of the carbon fiber prepared according to Example 2 was about 14.1 μm.

Example 3

A carbon fiber was prepared according to the same method as shown in Example 1 with an exception of using CPVC having a chlorine content of about 69 wt %.

Example 4

A carbon fiber was prepared according to the same method as shown in Example 1 with an exception of changing an average degree of polymerization of CPVC into 400 to 500.

Example 5

A carbon fiber was prepared according to the same method as shown in Example 1 with an exception of carrying out a preheating process under a nitrogen atmosphere by raising a temperature up to 300° C. at a heating rate of 3° C./min and heat-treating for 30 minutes.

Examples 6-7

A carbon fiber was prepared according to the same method as shown in Example 1 with an exception of carrying out an elongation process of the CPVC fiber having an average fiber diameter of about 51 μm at 120° C. and 150° C. respectively.

Comparative Example 1

A carbon fiber was prepared according to the same method as shown in Example 1 with an exception of omitting the elongation process of the CPVC fiber having an average fiber diameter of about 51 μm. An average fiber diameter of the carbon fiber prepared according to Comparative Example 1 was about 21 μm.

Comparative Example 2

An attempt was made to prepare a carbon fiber by applying electric spinning to the carbon fiber precursor solution of Example 1 instead of wet solution spinning in acetone.

However, in case of carrying out electric spinning according to this preparation method, it was difficult to obtain the CPVC fiber having an average fiber diameter of about 51 μm.

Evaluation Example 1: Thermogravimetric Analysis

A thermogravimetric analysis was performed on polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC). The thermogravimetric analysis was performed under an nitrogen atmosphere by using TGA 6300; (EXSTAR SII, SEIKO Co. Ltd., Japan) under the condition that a temperature was raised from 25° C. to 1000° C. (heating rate: 5° C./min) and nitrogen was supplied at about 200 mL/min. The results of the thermogravimetric analysis were shown in FIG. 1.

Referring to FIG. 1, CPVC was decomposed at 250 to 330° C. through dehydrochlorination to form polyene-type molecules, and was subjected(?) to a solid state carbonization process in a temperature range of 310 to 650° C. so as to form a 3D crosslinked and polycondensed aromatic compound. And it could be understood that the resultant compound is finally converted into a carbon material through heat-treatment at 650° C. or more.

Further, thermogravimetric analysis was performed on the CPVC fiber obtained by spinning a solution according to Example 1. The thermogravimetric analysis was performed by using TGA 6300; (EXSTAR SII, SEIKO Co. Ltd., Japan) under the condition that a temperature was raised from 25 to 350° C. (heating rate: 3° C./min and 5° C./min) and air was supplied at about 100 mL/min. The results of the thermogravimetric analysis were shown in FIG. 2.

Referring to FIG. 2, as a result of considering oxidative pyrolysis properties of the CPVC fiber, a weight loss mainly occurred at 220 to 350° C. and this result was the same as that of the thermogravimetric analysis performed on CPVC under the nitrogen atmosphere of FIG. 1. From the above results, it could be confirmed that CPVC is decomposed and converted into a carbon material through a solid state carbonization process.

Evaluation Example 2: Carbon Nuclear Magnetic Resonance Spectrum

¹³C-NMR analysis was performed on carbonized intermediate products in which chlorinated polyvinyl chloride (CPVC) and the CPVC fiber were carbonized at 1000° C. ¹³C-NMR was performed by using ECA400 (JEOL Co. Ltd.) and the results thereof are shown in FIG. 3. From this analysis, it is possible to understand a molecular structure and a carbonization yield of the intermediate products in which PVC, CPVC and CPVC fiber were heat-treated at 200° C., 300° C., 400° C. and 1000° C. under a nitrogen atmosphere.

Referring to FIG. 3, after heat-treatment at 1000° C., almost all the carbon groups of the CPVC fiber were changed into a carbon material and thus aromatic molecules accounted for about 99.2 wt %.

Evaluation Example 3: Scanning Electron Microscope

A scanning electron microscope (SEM) analysis was performed on the carbon fiber obtained according to Example 1 and the carbon fiber obtained according to Comparative Example 1. The SEM analysis was performed at an accelerated voltage of about 10 kV by using 6400F (JEOL Co. Ltd., Japan). The results of SEM analysis on the CPVC fiber obtained by spinning the solution according to Example 1 and the carbon fiber obtained according to Comparative Example 1 are the same as shown in FIGS. 4 and 5, respectively.

Referring to FIGS. 4 and 5, it could be understood that the carbon fiber obtained according to Example 1 has a very even surface in a very smooth state with almost no defects compared to the carbon fiber obtained according to Comparative Example 1.

Evaluation Example 4: Evaluation of Tensile Strength, Tensile Modulus and Elongation Rate

With regard to the carbon fibers prepared according to Examples 1 to 7 and Comparative Example 1, a tensile strength, tensile modulus and elongation rate were measured in accordance with JIS R 7606:2000 and the tensile strength was measured by using a strength testing apparatus: Tensilon UTM-11-20; Orientec Co. Ltd.).

The results of the tensile strength, tensile modulus and elongation rate are the same as shown in a following table 1.

TABLE 1 Tensile strength Tensile modulus Elongation rate Classification (MPa) (GPa) (%) Example 1 1400 87 1.6 Example 2 2050 128 1.6 Comparative 470 32 1.5 Example 1

As shown in Table 1, it could be understood that the carbon fiber obtained according to Examples 1 and 2 achieve a more improvement in the tensile strength and tensile modulus as well as a higher elongation rate compared to Comparative Example 1. Further, the tensile strength and tensile modulus of the carbon fibers of Examples 3 to 7 showed the results similar to those of Example 1.

Although the present invention has been described with reference to the above embodiments, they are set forth to illustrate only and those skilled in the art to which the present invention pertains will appreciate that various modifications and other equivalent embodiments are possible. Thus, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims. 

1. A carbon fiber having an average fiber diameter of 1 to 100 μm and prepared by spinning a solution of chlorinated polyvinyl chloride to obtain a chlorinated polyvinyl chloride fiber, elongating the chlorinated polyvinyl chloride fiber without an oxidative stabilization process, and preheating and carbonizing the elongated polyvinyl chloride fiber.
 2. The carbon fiber of claim 1, wherein the carbon fiber has the average fiber diameter of 10 to 20 μm, tensile strength of 1000 to 2500 MPa, tensile modulus of 70 to 140 GPa, and a degree of orientation of 60 to 80%.
 3. A method for preparing a carbon fiber having an average fiber diameter of 1 to 100 μm, the method comprising: spinning a solution of chlorinated polyvinyl chloride (CPVC) to obtain a chlorinated polyvinyl chloride fiber; elongating the chlorinated polyvinyl chloride fiber without an oxidative stabilization process to prepare an elongated chlorinated polyvinyl chloride fiber; preheating the elongated chlorinated polyvinyl chloride fiber at 150 to 450° C. under an inert gas atmosphere; and carbonizing the preheated product at 950 to 2000° C.
 4. The method claim 3, wherein a content of chlorine is 57.7 to 84.5 wt % and an average degree of polymerization is 400 to 800 in the chlorinated polyvinyl chloride.
 5. The method claim 3, wherein the elongating is performed by elongating the chlorinated polyvinyl chloride fiber at 120 to 150° C. with an elongation rate of 0.01 to 200%.
 6. The method of claim 3, wherein the elongating is performed by elongating the chlorinated polyvinyl chloride fiber at 120 to 150° C. with an elongation rate of 100 to 200%.
 7. The method of claim 3, wherein an average fiber diameter of the chlorinated polyvinyl chloride fiber is 30 to 100 μm. 